Rheostat



Nov. 10, 1942. F. E. RICH RHEOSTAT Filed Nov. 27, 1940 INVENTOR far/e52 [BL-h.

4 Q 3 a x a z e a Z. 2 a b a Q l I I I 1 J l 3 w 7% 1:5 [3 U 3 t u 1 4 0 mm S is F m h Z Patented Nov. 10, 1942 RHEO STAT Forrest E. Rich, Forest Hills, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Appiication November 27, 1940, Serial No. 357,427

4 Claims.

My invention relates, generally, to rhecstats, and it has reference, in particular, to rheestats having main and Vernier rheostat units.

In operating dynamo electric machines of different types, it is often desirable to utilize rheostats having different predetermined resistance curves conforming to particular characteristics of the machines so as to secure the proper control of the machines. Vernier rheostats are often utilized in connection with main rheostats to provide a plurality of relatively fine steps of resistance for accurately controlling the operation of a machine at any point in the operating range.

Where the steps of resistance of the main rheostat are equal throughout its operating range, it is a relatively simple matter to utilize a Vernier rheostat therewith. Where, however, the characteristics of the machine to be controlled require a main rheostat having unequal steps of resistance at different operating points thereof, it is not sufficient to merely connect a Vernier rheostat, having relatively fine resistance steps, in shunt or in series relation with the main rheostat. The Vernier steps under these circumstances bear different ratios to the steps of resistance of the main rheostat at different points in the operating range thereof, and uniform and definite control of the machine by the Vernier rheostat cannot thus be secured at different points in the operating range of the main rheostat.

Generally stated, it is an object of my invention to provide an improved rheostat having main and Vernier units which shall be simple and inexpensive to build and easy to operate.

More specifically, it is an object of my invention to provide for securing a substantially uniform ratio at any point in the operating range between the resistance steps of a Vernier rheostat and a main rheostat having a predetermined resistance curve with unequal resistance steps at different points in the operating range thereof.

Another object of my invention is to provide for securing uniformly increasing steps of resistance in the main rheostat unit and maintaining a substantially uniform ratio between said steps and the steps of a Vernier rheostat operatively connected with the main rheostat unit.

A further object of my invention is to provide for operatively connecting the movable contact Yet another object of my invention is to provide for so operatively connecting the main and Vernier movable contacts members of a rheostat having correspondingly tapered main and Vernier resistance steps as to maintain a substantiall definite predetermined ratio between the steps of the main and Vernier rheostat units throughout the entire operating range.

Still another object of my invention is to provide a rheostat having main and Vernier rheostat units so arranged as to secure a plurality of different predetermined ratios between the successive resistance steps thereof throughout the entire operating range.

In practicing my invention, a main rheostat unit having a plurality of increments or steps of resistance of different values connected between fixed contact members with a movable contact member for varying the effective number of said steps connected in a circuit and producing a predetermined substantially non-linear resistance curve may have associated therewith, an auxiliary or Vernier rheostat unit having a plurality of correspondingly different resistance steps or increments bearing a predetermined ratio to the corresponding steps of the main rheostat unit and a movable contact member for varying the effective number of steps thereof connected in the circuit. The contact member of the main rheostat unit may be cperatively connected to the contact member of the Vernier rheostat unit by lost motion connecting means so as to be actuated thereby to increase the number of effective steps of resistance in the main unit when the contact member of the Vernier unit has been advanced relative thereto a number of steps approximately equal to the ratio between the steps of the main and Vernier rheostat units.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following detailed description and the accompanying drawing, in which:

Figure 1 is a front elevational View of a rheo stat embodying the principal features of my invention;

Fig. 2 is a side elevational View of the rheostat of Fig, 1.

Fig. 3 is an enlarged cross sectional view taken along the line III-III of Fig. 2 showing one method of mounting the rotatabl contact arms;

Fig. 4 is a diagrammatic view showing the electrical connections between the main and Vernier units of a rheostat embodying my invention;

Fig. 5 is an enlarged elevational end view of the Vernier contact arm;

Fig. 6 is an enlarged rear view of a portion of the vernier contact arm showing one method of attaching the adjustable stop member thereto; and

Fig. 7 illustrates typical resistance curves of rheostats embodying the invention.

Referring to Figs. 1 and 2 of the drawing, the reference numeral I may denot a frame structure of any suitable type for supporting a rheostat panel I I on which may be positioned in concentric relation a plurality of spaced main and vernier contact members l2 and I3, respectively. Main and vernier movable contact members or arms l5 and I6 may be provided, being, for example, rotatably mounted on the panel by means of a shaft I! for engaging the contact members I2 and I3, respectively, so as to provide main and vernier rheostat units. A flexible conductor I8 may be provided for electrically connecting the contact arm I5 and I6.

In order to provide suitable encrements or steps of resistance between the successive contact members I2 and I3 of the main and vernier rheostat units, respectively, a plurality of resistance units I9 of any suitable type may be supported by the frame structure I0, being, for example, supported therein by means of tie rods which may extend horizontally between the side bars 22 secured to the frame structure, and be suitably spaced so as to engage slots 23 in the support members 24 of the resistance units. The resistance units I9 may be connected in series circuit relation so that the main and vernier resistance units are connected as shown in Fig. 4. The units I9 may also be provided with a plurality of suitable taps 25 for making connections thereto at different points. The contact members I2 and I3 may be connected by means of suitable conductors, of which only the conductors 26 and 21 are shOWn in order to avoid confusion, to the taps 25 on the resistance units, so as to provide suitably related increments or steps of resistance between successive contact members of the rheostat units, which may be connected in a circuit to be controlled by moving the contact arm I5 over the contact members to render the steps therebetween effective and produce the desired resistance curve for the main and vernier rheostat units.

The main contact members l2 may, for example, be so connected to certain taps 25 of the resistance units I9 as to provide substantially uniformly differing increments or steps of resistance between successive contact members in a counter-clockwise direction. For the purposes of convenience, instead of having the steps between successive contact members vary, the steps may be arranged in a plurality of groups, having, for example, four consecutive steps of resistance in each group of the same value, with the steps or increments in successive groups of substantially uniformly increasing values.

The vernier contact members I3 may be so connected to other taps 25 of the resistance units as to provide resistance steps or increments between the adjacent contact members arranged in groups with a corresponding taper, and having steps or increments bearing a predetermined ratio to the corresponding resistance steps or increments between the contact members l2 of the main rheostat unit at corresponding points. For example, the connections may be selected to provide ratios of 1/5, 1/10, or as desired, and the steps or increments of the vernier rheostat unit may be made to vary in the same proportion, or

Steps between Ohms contact per step members Ohms Steps between contact members per step wwcaocn The steps or increments of resistance between the vernier contact members may b arranged to produce a similar curve, with the steps or increments between the vernier contact members I3 bearing a predetermined ratio to the corresponding steps between the main contact members I2 at diiferent points. Where the ratio is 1/5, the vernier resistance curve should approximate the curve B of Fig. '7. Forty-nine vernier contact members may be used, so as to provide vernier adjustments for both the first and last main contact members, and the steps of resistance between the vernier contact members I3 may b as follows:

Steps Ohms between Ohms Steps between contact members per step Contact per Step members Where other resistance curves are desirable,

. the values of the resistance steps may be changed accordingly. For example, if it is desired to produce a main resistance curve such as the curve C of Fig. '7, the first few and the last few steps of resistance may be relatively large and may be approximately equal, so as to produce relatively steep linear portions a and c. Th intermediate steps may be relatively small, so as to produce a relatively fiat intermediate portion. With such a characteristic resistance curve, accurate regulation may be secured in five steps over the intermediate portion of th curve.

Other main resistance curves may be produced in accordance with the particular characteristics of the machine to be controlled, having different slopes at different points therein. By making the corresponding steps of the vernier element vary correspondingly to the main resistance steps, the vernier steps at any point always bear a predetermined ratio to th main steps, so that substantially the same degree of adjustment relative to the main steps can be secured on the vernier element at any point of operation.

Referring to Fig. 3 of the drawing, it may be seen that the vernier contact arm or movable contact member I6 may be provided with a hub 38 and secured by a pin 3| to the shaft H, which may be itself rotatably mounted by the bearings 32 in a bushing 33 projecting through the rheostat panel II and secured thereto by a nut 34. The movable contact member or arm I5 may be rotatably mounted relative to the shaft I'I, being, for example, provided with a hub 35 rotataly positioned on the hub 30 of the contact arm I6, and secured thereon by a washer 38 fastened to the shaft by a pin 31.

In order to secure relatively fine Vernier steps or increments of resistance throughout the operating range of the main contact arm 15, having a predetermined ratio to the corresponding steps or increments of the main rheostat unit at every point, the arms I5 and I5 of the main and Vernier rheostat units may be operatively connected by a suitable lost motion connecting means so that they may be maintained in predetermined relation relative to each otherthroughout the entire operating range.

As shown most clearly in Figs. 1, 2, 5, and 6, an adjustable stop member 38 may be positioned on the extended end portion 39 of the arm I6,

comprising, for example, an elongated body member 40 having a longitudinal slot 4| therein for receiving the threaded studs 42, whereby it may be adjustably secured to the extended end portion 39 of the contact arm by means of nuts 43 positioned on the studs. Means such as the upturned end portion 44 at one end of the body member 40 may be provided to engage the projecting end portion 45 of the contact arm I5 as the vernier arm rotates counterclockwise.

By sliding the stop member to adjust the relative position of the stop member 38 on the contact member IS, the upturned end portion 44 may be made to engage the projecting end 45 of the contact arm l5 when the Vernier contact arm I6 has reached different predetermined positions in advance of the main contact arm I5. These positions may be determined by advancing the contact arm It a number of fixed contacts in advance of the contact arm I5 equal to the particular ratio between the steps of resistance in the main rheostat unit and the Vernier rheostat unit.

Thus when the Vernier contact arm I6 is moved relative to the contact arm I5 a sufficient number of contacts I3 to render effective, or connect in a circuit additional steps or increments of resistance equal to that between the consecutive contacts I2 of the main rheostat unit, the contact I5 will then be actuated by means of the adjustable stop member 38 in response to continued movement of the Vernier arm IS in the same direction. If the ratio between the steps of resistance in the main and Vernier units is 5:1, then the Vernier arm should advance 5 contacts before the stop member 38 engages the main contact arm I5. For other ratios of resistance the stop member may be adjusted accordingly.

Means such as the handle 4] may be provided for actuating the Vernier contact arm I6, and a stop member 48 may also be provided for engaging the roain contact arm I5 to actuate it when the vernier arm is moved in a clockwise direction. Stationary stops 49 and 58 may be provided for engaging the main contact arm I5 at the limits of its operating range.

It will be understood that the stop members 38 and 48 effect movement of the main contact arm I5 in response to movement of the Vernier contact arm I6 in opposite directions. It is immaterial for the purpose of the invention in which directions the particular stop members actuate the contact arm I5. The Vernier arm may, if desired, be op'rated by any suitable actuating means connected to the shaft H, such as is customary in automatic regulator systems.

From the above description and the accompanying drawing, it will be apparent that I have provided in a simple and effective manner for securing Vernier adjustments to a main rheostat unit having unequal resistance steps at different points of the operating range. By utilizing my invention, smooth and accurate control of a dynamo electric machine may be obtained throughout the entire operating range of the main rheostat unit, as Vernier steps are provided which always have a predetermined ratio with respect to the main steps of the resistance at any point in the operating range. A wide range of different ratios may easily be provided with a rheostat constructed in accordance with my invention by adjustment of the lost motion connecting means and the connections of the fixed contact members to the resistance units.

Since certain changes may be made in the above description and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing, shall be considered as illustrative and not in a limiting sense.

I claim as my invention:

1. The combination in a rheostat, of a main rheostat unit having a movable contact member and a resistance element with fixed contact members connected thereto arranged to provide different increments of resistance therebetween at different points to produce a predetermined resistance curve, a Vernier rheostat unit having a movable contact member and a resistance element connected in series with the main element having fixed contact members arranged to provide correspondingly different increments of resistance therebetween having approximately a predetermined ratio to the corresponding increments of resistance of the main element, and lost motion connecting means 0peratively connecting the main and. Vernier movable contact members having stop means so positioned relative to each other as to move the main movable contact member in response to movement of the Vernier movable contact member when the Vernier movable contact member reaches a position a number of fixed Vernier contact members in advance of the main movable contact member, said number being substantially equal to the ratio between corresponding increments of resistance of the main and Vernier rheostat units.

2. A rheostat comprising, a main rheostat unit having a resistance element with a plurality of spaced contacts connected thereto to provide substantially uniformly varying steps of resistance between successive contacts and a movable contact member for engaging the contacts, an auxiliary rheostat unit having a resistance element with a plurality of taps and a plurality of spaced contacts adjustably connected therewith to provide substantially uniformly varying steps of resistance between successive contacts having different definite ratios to the corresponding resistance steps of the main unit at given operating points throughout substantially the entire operating ranges of the rheostat units and a movable contact member for engaging the contacts, and adjustable means operatively connecting the main movable contact member to the auxiliary movable contactrmember adjustable for different ratios of resistance between correspondlng contacts of the main and Vernier units to move the main contact member in response to movement of the auxiliary contact member when the auxiliary contact member has been moved a predetermined number of contacts relative to the main contact member equal to the ratio between the corresponding steps of the main and Vernier rheostat units.

3. A composite rheostat comprising, a frame, a panel supported thereby, a plurality of resistance elements, a plurality of spaced fixed contact members arranged on the panel and connected to the resistance elements to provide main and Vernier resistance elements connected in series relation and with a plurality of correspondingly differing steps of resistance connected between successive contact members to provide corresponding substantially non-linear resistance curves, the steps of the Vernier element bearing a predetermined ratio to the steps of the main element at corresponding operating points, a movable contact member for engaging the fixed contact members of the Vernier element, a movable contact member for engaging the fixed contact members of the main element, and lost motion connecting means operatively connecting the main and Vernier movable contact members so that the former is moved in response to movement of the latter when the Vernier contact arm reaches a position a predetermined number of steps in advance of the main contact member substantially equal to the ratio between the corresponding steps of the main and Vernier elements.

4. A rheostat comprising, a main rheostat unit having a plurality of fixed contact members arranged in predetermined formation with steps of resistance connected therebetween of increasing value from one end of the operating range to the other and a rotatable main contact arm actuable to vary the effective number of said steps connected in a circuit to be controlled, a Vernier rheostat unit having a plurality of fixed contact members concentrically positioned relative to the main contact members with correspondingly increasing steps of resistance connected therebetween having a predetermined ratio to the corresponding steps of the main rheostat, a Vernier contact arm rotatably mounted on the main contact arm and electrically connected thereto, and lost motion means so connecting the main contact arm to the Vernier contact arm adjustable for different ratios of main and Vernier steps so that the main contact arm is actuated thereby when the Vernier arm reaches a position a number of contact members in advance of the main contact arm approximately equal to the ratio of the steps of resistance connected between the main and Vernier contacts at that point,

FORREST E. RICH. 

